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Trap-Assisted Charge Injection into Large Bandgap Polymer Semiconductors
Dongdong Wang1,2, Michael Fina3, Suhan Kim4
1Beijing Institute of Graphic Communication, Beijing 102600, China.
Materials (Basel, Switzerland)
|August 2, 2019
Summary
Inserting lithium fluoride (LiF) into polymer light-emitting diodes enhances both electron and hole injection, particularly improving hole injection. This LiF layer also stabilizes internal interfaces, boosting device performance.
Area of Science:
- Materials Science
- Organic Electronics
- Device Physics
Background:
- Organic light-emitting diodes (OLEDs) rely on efficient charge injection for optimal performance.
- Polyfluorene and poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) are common materials in OLED fabrication.
- Trap-assisted charge injection can limit device efficiency.
Purpose of the Study:
- To investigate the effect of lithium fluoride (LiF) insertion on charge injection in OLEDs.
- To analyze the impact of LiF on internal interfaces within the device structure.
- To compare experimental findings with numerical simulations to understand underlying mechanisms.
Main Methods:
- Fabrication of OLED model systems using polyfluorene and PEDOT:PSS with Al or Al/LiF cathodes.
- Transmission electron microscopy (TEM) to observe internal interface evolution.
- Numerical simulations using a revised Davids model for charge injection analysis.
Main Results:
- A 1.3 nm LiF insertion simultaneously increased both electron and hole injections.
- The increase in hole injection was more significant than the increase in electron injection.
- LiF introduction improved interface stability at the cathode/polymer and ITO/PEDOT:PSS interfaces.
- Experimental results were consistent with numerical simulations.
Conclusions:
- LiF is an effective material for enhancing charge injection and improving interface stability in OLEDs.
- The study provides insights into the physical mechanisms of trap-assisted charge injection.
- Optimizing LiF layer thickness and integration can lead to more efficient organic electronic devices.
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